The fact that enamel thickness varied widely in Leslea's baboons also sounded a warning call for scientists studying hominids in the fossil record. Leslea points out that "in this field, people get in very serious debates over extremely minor variation." To a paleoanthropologist studying an extinct hominid lineage, a fossil with tooth enamel ½mm thicker than another might be considered a new species. But Leslea's data suggest that such a small difference could easily reflect natural variation within a single population: "It was like, 'Wait a minute  you guys are making a really big deal over ½mm difference in enamel thickness, and I've got that much variation in all these baboons that are related!...Our point is that just because you have a ½mm difference between two fossils, that difference doesn't necessarily make this one a chimpanzee and this one a hominid. You have to be more careful about this particular trait."

That's not to say that differences in tooth enamel are meaningless. A half a millimeter of tooth enamel could make the difference between one hominid species and the next, but in order to support that argument, you'd first need to understand the naturally occurring variation within that population by examining many different examples of the fossil species.

And that brings us back to Leslea's work relating to human evolution...

Leslea's research has important implications for how paleoanthropologists distinguish species  but it also has important implications for how biologists reconstruct the evolutionary relationships among those species. Dig deeper in Teeth and the hominid tree.